IOI 2019 took place in Azerbaijan, from August 4-11, 2019. More info is available on the official website.
Just finished IOI 2019 in Azerbaijan
The 1st International Olympiad in Informatics was held in Pravetz, Bulgaria, from May 16-19, 1989. Six problems were presented to the jury of the event. The first problem (shown below as "Problem 1") was selected for the competition.
Note that the grading model changed at IOI'94 and beyond.
Before IOI 1994, a human evaluator would sit behind the competitor's computer and do the testing manually (enter test data through the keyboard, check the output on the screen). Starting from IOI 1994, an automatic grading process is used, with test input defined in files.